In an indoor or public space environment, there is a need for a communication system able to dedicate applications (for example, access to specific services) on the basis of the location of a user (more precisely, a user station). A problem is to localize the stations in the environments with respect to physical areas to which dedicated proximity based application(s) are related.
Many outdoor localization techniques are known. For example, the GPS (Global Positioning System), the triangulation from earth fixed transceivers, the radio angle measurements, are efficient outdoor localization systems. However, such systems are unable to perform an indoor (in-building) localization due to the shielding resulting from walls and radioelements. Such perturbing elements that can also be present outside render the above systems not very precise even outdoors.
A first known indoor localization system uses fixed infrared transceivers located in a building. The system determines in the field of which transceiver is the object and considers this field area as the location. A drawback of such a system is that many infrared fixed transceivers have to be installed in the building due to the poor range of IR access points, and their limitations to being line-of-site. Further, such a system has to be dedicated to the localization. Additionally, the data carrier bandwidth of IR-systems is not sufficient for most of the applications of wireless system for which the required transmission rate becomes higher and higher.
Recent indoor communication systems use radiofrequency transmission. Such systems provide fixed access points to the wireless communication network, which are distributed inside the building or public space to be covered. A station is connected to the network through the access point from which it receives the higher signal strength. This determination is made by the station itself which examines the signal levels received from the different access points, and then chooses one of these to communicate with to access network resources. The network routing protocol takes into account the access point choice of the station in order to switch the communication to the right access point. Of course, such systems also work outdoors, and at least a part of the access points can be located outdoors. For example, networks in accordance with the standard 802.11b to which the present invention applies more particularly belong to this type of systems.
Recently, some of these systems have been provided with a localization function of the stations, that is a determination of the physical location (and not only the determination of the access point to be connected to).
An example of such in-building radio-frequency wireless network system is described in the article “A Software System for Locating Mobile Users: Design, Evaluation, and Lessons” by Paramvir Bahl, Venkata N. Padmanabhan and Anand Balachandran, published in December 2000, published at http://www.cs.ucsd.edu/users/abalacha/research/papers/msr-tr-2000-12.pdf as of November 2001. In that system, a history-based station-tracking algorithm takes into account the motion of the user station in order to follow this motion from an access point to another using a pre-determined and configured database representing a static signal strength map in principle.
Another example is described in the article “Determining User Location for Context Aware Computing Through the Use of a Wireless LAN Infrastructure” by Jason Small, Asim Smailagic and Daniel P. Siewiorek, published in December 2000, published on http://www-2.cs.cmu.edu/˜aura/publications.html. Such a system uses a triangulation technique based on signal intensity from wireless access points.
US 2001/036833 discloses a localization system in which the mobile stations monitor the electric field intensity received from a plurality of repeaters. The mobile stations transmit to a central server the measured intensities. The central server localizes the mobile stations according to wave propagation pattern information contained in the central server.
WO 00/38460 discloses a localization system in which mobile stations transmit identity information at a predetermined power level. Localization beacons receiving this information respond to the mobile stations only if the received signal level is higher than a predetermined threshold.
A purpose of the present invention is to provide another localization method and system.
Another purpose of the present invention is to provide such a localization method and system particularly adapted to dedicate application(s) to the relative location of the stations.
Another purpose of the present invention is to provide such a method and system which do not need structural hardware modification of the existing mobile stations, wireless access points and central server.
Another purpose of the present invention is to provide a communication method and system between mobile stations and at least one central server through a radio-frequency wireless network, using proximity based applications.
Another purpose of the present invention is to provide a method and system adapted to omnidirectional RF system and, more particularly, to one unregulated spectrum standard suites.